Sex Influences the Genetic Structure of Greenland Halibut in the North Atlantic

Greenland halibut (Reinhardtius hippoglossoides) is a commercially important species in the North Atlantic whose spatial population structure has not yet been fully determined across its entire range. We genotyped individuals from across the North Atlantic using a subset of informative single nucleotide polymorphic (SNP) markers to assess their usability as a SNP panel. We assessed whether these purportedly structured SNPs had any association with sex. We found several of these loci to be in sex-determining chromosomes and that their inclusion generated genetic structure mainly in males. The population structure without the sex-associated SNPs was weak and followed an isolation-by-distance pattern, likely with a large regional population on each side of the North Atlantic. We discuss how different sex ratios in the samples and/or an evolving sex-determination system in this species likely caused the inclusion of sex-associated loci in the panel. We found suggestive evidence of polymorphisms at sex-determining chromosomes differentiating males on east and west locations, indicating evolution of the sex-determination system. These results highlight the importance of documenting sex-based differences in genetic studies and call for a better understanding of genomic architecture to understand sex-determination systems across the whole distribution of sexually dimorphic species.